KDXRIDER.NET

It’s been one thing after another since I brought my KDX home. I knew it was a project when I bought it, but when I test rode it, the front brakes worked fine. Now, not so much.

I have been putting fork seals and bearings in the front end and am trying to get it all back together. Part of that was new brake pads, since the old ones were oil soaked due to the bad fork seals. I had a hard time getting the pistons pushed back in (with the bleeder open), but got them pushed in just far enough so the rotor would fit between the new pads. Then I figured I would replace the brake fluid using a Mity-Vac, just like I have done many time in the past on other bikes.

I cracked the bleeder, took the master cylinder cover off, and drew a vacuum. The vacuum held and it would not draw any fluid through the system. The lever was limp and it would not compress the brake pads.

I had the bleeder loose enough I was surprised the vacuum didn’t leak down through the threads. I removed the bleeder screw and hand pumped the brake, covering the bleed hole when the lever was returning. It sucked a little fluid out of the reservoir but it wasn’t moving nearly as much fluid as I would have expected.

I cleaned the bleeder screw and took the brake line off at the master cylinder and put that end of the brake line in a jar of brake fluid. Using the Mity-Vac, I was able to pull fluid through the line and caliper without an issue. Both banjo screws are passing fluid fine.

So I thought the problem was narrowed to the master cylinder. I took it apart expecting to see an issue but did not. The bore looks fine. There is no corrosion, and the cup seals seemed to seal well against the bore when I slipped the spool back in. I blew air through the bore to clear any potential clogging of the relief and supply ports in the master cylinder. The odd thing is, the manual shows two separate ports, but I can only see one in my master cylinder. Since the brakes worked earlier and apparently worked fine for the previous owner, I’m assuming this is not an issue.

So I don’t know what else the problem could be. The caliper is getting rebuilt since I am this far into it. I blew the pistons out of the caliper with compressed air. They were tight and when they exited their bores they made a heck of a loud pop. I don’t know if that is typical or not.

I am convinced the problem is with the master cylinder, but I don’t know what the issue might be with it. The bleeding process described in the service manual talks about stroking the lever till there are no air bubbles seen in the fluid reservoir, which I have done. Is there any other way to bleed the master cylinder that I am missing? It seems like there is air in the system.

With the cylinder assembled, full of fluid, bled (as far as I know), but off the bike and not hooked to the brake line, when you squeeze the lever nothing comes out of the brake line port. I’d expect it to shoot fluid out. There is no resistance to the lever pull except the return spring (when its all hooked up).

Anyone have any ideas? I’m certainly no expert at this so I could be missing something pretty obvious. Thanks in advance.


turtle

I say there was no problem to begin with. You just needed to push the fluid up through the bleeder to the master cylinder.

There will not be any pressure on the lever unless the cap is on and there is no air in the system. If you think about it.... what would it have pressure against?

Inda, thanks for the response. I am sure I have missed something here.

Couple ?'s tho - how would you push fluid up through the bleeder and into the m/c? Shouldn't I be able to draw fluid from the m/c down through the caliper and out the bleeder to accomplish the same thing (keeping the reservoir full of course)?

What is the best way to bleed the m/c and rest of the system to make sure I have every bit of air out? Following what I have used in the past and what is in the manual doesn't seem to be working.

At least I am learning!

TIA

Use a syringe and push the fluid up from caliper to the MC. Seems to work best.

A Catheter syringe that you can buy at any medical supply place and a piece of clear tubing which can be got at a home improvement place that will fit over the bleeder and syringe.... Once you push the fluid out of the syringe, lock down the bleeder and refill the syringe... and do it again... that's all it should take. You don't have to worry about the master cylinder level since it will overflow with fluid...

Works so fast your head will spin....

Sweet. I'll give it a shot. Thanks guys.

the syringe method works great. you can also draw the fuild instead of pushing it up. it wont overflow on the master cylinder without you knowing. just have to keeping adding the fuild to the master.

KDXsg wrote:you can also draw the fuild instead of pushing it up. it wont overflow on the master cylinder without you knowing. just have to keeping adding the fuild to the master.

That was the original problem that got me looking into the rest of the system. I could not draw the fluid through the system from the reservoir using a Mity-vac on the bleed screw.

I can't try pushing the fluid till I get my caliper rebuild kit and get the caliper back together but I'd like to know sooner rather than later ... am I going to be able to push it up through the system?? KDXsg's comment makes me wonder ...

Never do the draw... that has NEVER worked for me... only the push....

Indawoods wrote:Never do the draw... that has NEVER worked for me... only the push....

10-4, dood. Thanks.

I have taken alot from this site and just trying to give some back. The drawing have always worked for me. also I have been servcing my buddies bikes using this method. maybe it just works ONLY for me not anyone else....haha...Heya turtle...maybe keep this method as the last resort if every other methods fails.

I used a Mity-Vac to do the draw method and all I ever got was bubbly fluid... I could never get just solid fluid out of the bleeder.... if it works for you...that's a good thing.

ohh...maybe thats why got confused. i meant using a large catheter syring to draw the fuild from the bleeder valve. not using the Mity-Vac.

Indawoods wrote:I used a Mity-Vac to do the draw method and all I ever got was bubbly fluid... I could never get just solid fluid out of the bleeder.... if it works for you...that's a good thing.

I have had trouble on other bikes drawing bubbly fluid, so I get what you are saying, but in this case I can't pull ANY fluid - nada. That's what is making me wonder. The Mity-vac held a vacuum for several minutes and never drew a drop, bubbly or otherwise.

I still wonder if something else is wrong. I'll see if I can push fluid when I get it back together, but I am having my doubts ....

It is usually the bleeder being clogged if you have that problem. I have had to clean more than one....

It's clean (unfortunately).

From my original post: "I cleaned the bleeder screw and took the brake line off at the master cylinder and put that end of the brake line in a jar of brake fluid. Using the Mity-Vac, I was able to pull fluid through the line and caliper without an issue. Both banjo screws are passing fluid fine. "

So I have been able to pull fluid through the entire system except for the master cylinder. Are there supposed to be two holes in the bore of the master cylinder? The manual talks about a supply port and a relief port. I can only see one port in there. I dunno. Grasping at straws here. The brakes worked when I test rode the bike and apparently worked fine for the PO.

I have never had any issues with a master cylinder except on a old Triumph 750 Bonneville I have.

I have never had to tear into the KDX's master cylinders so I don't know much about them except they work....

Just for what it's worth, I just changed the brake fluid in my front brakes and I tried the methods listed above with little success, pushing or pulling. So what I did was
Step 1: get a bunch of beer.
Step 2: fill the master cylinder.
Step 3: open the bleed screw.
Step 4: wait until the master cylinder gets low.
Step 5: refill the master cylinder.
After about 4-5 beers (may take up to 18 if it is hot out) of keeping the master cylinder full I closed the Bleed screw and replaced the master cylinder cover, pumped the brakes and they were right there. Test run proved that it was successful.
Maybe I just got lucky but i'll take luck over skill any day.

aint that called gravitiy bleeding???

>|<>QBB<

kdxmaniac wrote:aint that called gravitiy bleeding??? :grin:

You are absolutely correct! But from my experience it doesn't have to be hard for it to work. Dose it?